The vocal organ of birds is the syrinx. It includes two sound sources, one in each bronchus. The left syringeal half, under the control of the left hypoglossus, is responsible for most or all song components in the canary. The left hypoglossus is controlled predominantly by the left hemisphere, which thus furnishes an intriguing example of hemispheric dominance, and the only known instance of this phenomenon other than in man. The proposed research will probe further into the nature of this dominance, trying to discover whether parts of the brain that store or process auditory inputs also have a dominant side, as described for the efferent vocal control system. We shall also test whether recovery of song following left hypoglossal section is enhanced by subsequent lesion of the ipsilateral hyperstriatum caudale, pars ventrale (HVc), known to control syringeal output in birds such as the canary. We shall also explore histological ways of recognizing and quantifying differences in the characteristics of the brain vocal control areas of both hemispheres. Such differences might prove useful correlates for timing the functional reversal of hemispheric dominance which follows left HVc lesion. Bibliographic references: Stokes, T.M., C.M. Leonard and F. Nottebohm. 1974. The telencephalon, diencephalon, and mesencephalon of the canary, Serinus canarius, in the stereotaxic coordinates. J. Comp. Neurol. 156:337-374.